This invention relates to an exhaust treatment for an outboard motor, and more particularly to an improved catalytic exhaust system for such outboard motors.
The desirability of effectively controlling the amount of harmful exhaust gas constituents in internal combustion engines are well known. These goals are particularly desirable in conjunction with outboard motors wherein the exhaust gases are discharged not directly to the atmosphere but through the body of water in which the associated watercraft is operating. As a result of this, not only is there a danger of air pollution from undesirable exhaust gas constituents but also a problem in conjunction with possible water pollution.
Although many steps are taken in the basic design of the engine to ensure good fuel efficiency and effective exhaust gas treatment, under some instances it is desirable to also employ catalysts in the exhaust system for treatment to reduce certain harmful exhaust gas constituents. As is well known, these catalysts operate at relatively high temperatures in order to be fully effective, and their efficiency depends upon their temperature.
As has been previously noted, it is the normal practice in marine propulsion units to discharge the exhaust gases to the atmosphere through the body of water in which the watercraft is operating. This is particularly desirable because most marine propulsion systems do not offer sufficient space for full engine exhaust silencing. By discharging the exhaust gases to the atmosphere through the body of water in which the watercraft is operating, further silencing can be obtained.
However, the use of such underwater exhaust gas discharges can present some problems, particularly where catalytic exhaust systems are employed. The water level within the exhaust system can change quite abruptly during engine operation. For example, when the watercraft is traveling at a high speed and is in a planing condition, the underwater discharge and exhaust system is relatively shallowly submerged. The exhaust gas pressure is high enough so as to ensure that water cannot enter backward through the exhaust system and come into contact with the catalyst.
If, however, the boat is abruptly decelerated, then the boat and its propulsion system becomes more deeply submerged in the body of water in which the watercraft is operating. In addition, at this time the exhaust pressure falls off, and water can easily flow back into the exhaust system through the underwater exhaust gas discharge. If this water comes into contact with the catalyst, the catalyst may become polluted and inoperative or, alternatively, have its efficiency deteriorated. In a worst case situation, the catalyst bed may actually become shattered or damaged due to the impacting of water on it at its elevated temperature and the fact that many catalyst beds are of ceramic-type material. These problems are particularly acute in operating in salt-water environments as the salt in the water may offer further fouling of the catalyst.
It is therefore a principal object of this invention to provide an improved exhaust treatment for an outboard motor.
It is a further object of this invention to provide an improved arrangement for protecting an outboard motor and its catalytic exhaust system from damages or inefficiency under all running conditions.
It is a further object of this invention to provide a catalytic exhaust system for a marine propulsion unit wherein it would be ensured that the water through which the exhaust gases are discharged cannot reach the catalytic bed.
Even in marine exhaust systems that do not include catalytic treatment in the exhaust gases, there is a desirability to ensure against water encroaching into the exhaust conduit above a predetermined point. As is well known, there are times when the exhaust pulses may produce actually a negative pressure at the discharge end of the exhaust pipe that conveys the exhaust gases to its underwater exhaust gas discharge. If water can reach this level under such conditions as extreme deceleration, then there is a risk that the water can actually enter into the engine through its exhaust port. This is obviously undesirable.
It is therefore a still further object of this invention to provide an improved exhaust system for a marine propulsion unit wherein it is ensured that water cannot enter the engine through its exhaust ports.
It is a further object of this invention to provide an improved system for protecting against undue rise in the water level in the exhaust system of an outboard drive.